The invention relates to a circuit arrangement for the periodic testing of the operating reliability of an electronic antiskid control system which, by means of appropriate control signals, influences the pressure-medium operated brake device of a vehicle, in particular of a road vehicle, by energizing or de-energizing the magnet of an electro-pneumatic modulator valve.
In such systems it is necessary, from time to time or also continually during various operating conditions of a vehicle, such as during braking, to check the operating reliability of the electronic switching means, which serve the purpose of controlling the modulator valve solenoids.
In order to meet these requirements it is known to use a monitoring device wherein by short-circuiting speed sensors there is generated a simulated control signal, followed by checking as to whether the system responds to the signal so produced.
In such a device it is a disadvantage that such control signals, which thus simulate a locking of the respective wheel, can be produced only above a certain wheel or vehicle speed, and for this reason it is not possible to perform a checking at lower speeds.
There is also known a circuit arrangement for checking the operating reliability of an antiskid control system which enables a checking as to the proper functioning of the antiskid system only before starting to drive. With this antiskid control system it is a disadvantage that there is no possibility of checking while driving.
Generally, the known arrangements provide for only one monitoring possibility with respect to an inadmissible switching time. Accordingly, in this way an error is only detected after the inadmissible switching time and not beforehand.